1. Field of the Invention
The present invention relates to a projection display apparatus employing eflection-type liquid crystal display devices.
2. Description of the Prior Art
Conventionally, various display apparatuses of the so-called projection type have been proposed. For example, Japanese Laid-Open Patent Application H2-74903 proposes an arrangement that employs an optical system in which illumination light is separated into beams of different colors and these beams are integrated together by a color integration system including a polarizing beam splitter, a liquid crystal display device, and a cross-dichroic prism. Japanese Laid-Open Patent Application H8-122772 describes, as prior art, an arrangement that employs an optical system composed of three reflection-type liquid crystal display devices, a polarizing beam splitter, and two dichroic mirrors. This Japanese Laid-Open Patent Application H8-122772 proposes an arrangement that employs an optical system composed of three reflection-type liquid crystal display devices and a polarizing beam splitter.
However, the above-mentioned optical system including a cross-dicliroic prism is unduly expensive, because the cross-dichroic prism itself is expensive. The above-mentioned optical system having three reflection-type liquid crystal display devices, a polarizing beam splitter, and two dichroic mirrors requires that the two dichroic mirrors be disposed between the polarizing beam splitter and the reflection-type liquid crystal display devices. This makes the back focal length, i.e. the distance from the projection lens to the reflection-type liquid crystal display devices, unduly long, and thus makes the f-number of the projection lens unduly large, making it impossible to obtain satisfactory brightness.
The above-mentioned optical system proposed in Japanese Laid-Open Patent Application H8-122772 lets unpolarized light enter the polarizing beam splitter, and therefore suffers from flare caused in the projected image by unused polarized-light components. Moreover, this optical system discards the P-polarized light component included in the green component and the S-polarized light component included in the red and blue components without using them for image formation, and thus suffers from inefficient use of the light source.